1. Field of the Invention
The present invention relates to a method of forming aluminum nitride (AlN) film on the surface of substrates and more particularly relates to a method of forming aluminum nitride (AlN) film on the surface of substrates for use in the manufacture of electronic circuit substrates, optical parts and components, magnetic recording media and related articles of manufacture.
2. Description of the Prior Art
Several methods of forming aluminum nitride film on the surface of substrates have been proposed One method comprises chemical-vapor deposition (CVD) using reactive gas, for example, AlCl.sub.3 + NH.sub.3 or AlBr.sub.3 + NH.sub.3. Another method comprises ion plating in which aluminum is ionized, for example, in an NH.sub.3 gas atmosphere and deposited on a substrate using an electric field Still another method involves the sputtering method in which an aluminum target is sputtered, for example, in an NH.sub.3 gas atmosphere.
In all of these prior art methods, however, it is generally necessary to heat the substrate to a high temperature, i.e. approximately 1000.degree. C. in order to obtain a high-quality aluminum nitride film. Accordingly, the choice of materials which are suitable for use as substrates is severely limited
Another drawback of these prior art methods is the problem associated with impurities. Gaseous impurities such as Cl.sub.2 and H.sub.2 are apt to become mixed and incorporated into the aluminum nitride film. Additionally, unionized aluminum may be taken into the aluminum nitride film, particularly in the ion plating method. These impurities cause changes in the composition ratio of aluminum (Al) and nitrogen (N) in the aluminum nitride film and thereby deteriorate the various physical properties of the aluminum nitride film, such as, for example, optical characteristics and electrical resistivity. The consequence is that the desired aluminum nitride film is not produced, and the aluminum nitride film that is formed has unpredictable and undesirable physical characteristics.